Conventionally, metallic materials have been widely used as materials for mechanical parts as utilizing various material characteristics of the metallic materials. Further, needs for mechanical parts have been increasing with recent row progress in the technology, and mechanical parts using non-metallic materials such as sintered ceramics or plastics have often been utilized to supplement defects of the metallic materials. However, while the technological innovations have been progressively effected, it is an actual situation that all the needs cannot be supplemented by the conventional materials. Therefore, new materials particularly having excellent cutting and grinding workability that can be used for new mechanical parts have been demanded.
Meanwhile, paper feed rollers in printing machines such as printers, facsimile machines and copying machines are generally made of metals in such a structure that their surfaces are edged or coated with a paint to increase a frictional coefficient. Recent higher accuracy tendency of the printing machines has increased demands for the accuracy paper feeding. Particularly, in the color ink jet type printer, etc., the accuracy in feeding both the ink particles and papers needs to be controlled in an order of microns to improve the power of expression of photographs. It is known that increase in the diameter of the paper feed roller is effective to enhance the paper-feeding accuracy.
For example, it is expected that the 36 mm-diameter roller has the paper-feed accuracy of 3 times as much as that of the 12 mm-diameter roller.
However, if a large-diameter roller is to be made of a conventional metal, it is clear that it is more difficult to cut its part in this case as compared with a small-diameter roller, that among other things, it is extremely difficult to entirely finish grinding it in an error range of a micron order, and that the production requires a huge cost It is also clear that increase in the diameter of the metallic roller gains the weigh In this case, it is impossible to control the roller by means of the conventional driving mechanism, that is, a motor, gears, etc. for the small diameter roller. Further, it is necessary to effect the entire change in design and the reinforcement of the driving motor and the gear wheels. This directly leads to large increase in not only the weight but the cost of the entire product.
As mentioned above, although the increase in the diameter of the roller enhances the paper-feed accuracy and can consequently provide a product having high accuracy power of printing expression, it is difficult to attain this with the conventional metallic materials at a low cost.
Many techniques have been disclosed to form ceramic layers on surfaces of rotary bodies. For example, JP-A 3-7668 and JP-A 8-73094 disclose paper feed rollers in which a film is formed on a surface of a metallic cylindrical roller portion by flame spraying. However, the ceramic flame spraying is not suitable for obtaining large-diameter rollers. Further, JP-A 61-23,045 discloses a paper feed roller composed of an inner portion of an elastic body layer and an outermost portion of a ceramic layer. It is pointed out that increase in the thickness of the ceramic layer peels the ceramic layer from the elastic body layer.
Further, JP-A 1-261,159 discloses a structure in which a sintered ceramic outer layer and a metallic inner layer are preliminarily prepared and the sintered ceramic outer layer is externally fitted around the metallic inner layer for a roller in a copper foil-producing roller. If the sintered ceramic outer layer is used in this manner, the method must be employed to separately mold a ceramic body, sinter it, and fitting or bonding the sintered body into the rotary shaft. Further, if the roller is to be grindded to enhance the accuracy of the roller, it is difficult to grind it without relying upon a grinding stone of such as diamond because the roller is hard, and the working speed will be extremely low. This will increase the cost.
JP-A 10-16,326 discloses that a compounding mixture is obtained by mixing a defoaming agent, a tackifier, an inflating agent, a curing promoter, etc. with main components including cement, aggregate and a flowing agent, a flowing fill-in mixture is obtained by kneading the compounding mixture with water, filling the flowing fill-in mixture into a mold in which a core rod is inserted, cured and hardened to obtain a core member for a platen, and the core member is press fitted into a cylindrical rubber, followed by grinding the surface of the rubber if necessary. According to WP-A 1052,951, the same flowing fill-in mixture is filled in a space between a core rod and a cylindrical rubber as an outermost peripheral portion, and cured and hardened to obtain a platen. Since the flowing fill-in mixture is used to mold the platen core member, designing in the compounding mixture is complicated, which leads to increase in cost.
JP-A 8-324,047 discloses a light-weight and noise-preventing roller for an image-forming apparatus, which is obtained by filling a flowing solidifiable material such as a ceramic material including cement in a space between a rotary shaft and a surface layer made of hard rubber. Since it is difficult to cut the surface of the hard rubber at high accuracy, the above roller cannot be employed as a roller requiring grinding for attaining high accuracy.
Further, since a large amount of water is used to cast cement, etc. into a mold, the molded body suffers from a volumetric change through removal of water, which causes insufficient shape and dimensional stability and does not fit high accuracy.
Therefore, no structure has been available for such paper feed rollers, which satisfy “light”, “inexpensive”, “highly accurate” and “easy to design a gear portion” without effecting large design changes upon the paper feed mechanism for the conventional paper feed rollers, and appearance thereof have been eagerly desired.